High platelets in children, firstly, physiological factors should be considered, such as different times and seasons will lead to slight changes in platelets, and the platelets will also be higher in the exercise state than in the quiet state. Secondly, pathological factors should be considered as the cause, and the cause should be clarified and treated symptomatically. There are many causes of increased platelets in children, the more common ones clinically are dehydration, infectious diseases, immune diseases and myeloproliferative diseases. 1. Dehydration: caused by insufficient body fluids and blood concentration in children. If children drink less water or suffer from gastrointestinal diseases, they will have symptoms such as vomiting and diarrhea. More body fluid is lost and dehydration easily occurs, which leads to blood concentration and causes high platelet count; 2, infectious diseases: such as the occurrence of upper respiratory tract infections, pneumonia, sepsis and other infectious diseases, due to the stimulation of toxins, making bone marrow proliferation very vigorous, resulting in excessive platelet production, there will also be a high platelet count; 3, immune diseases: suffering from autoimmune diseases, such as Kawasaki disease in children, skin mucous membrane Lymph node syndrome, etc., are prone to high platelet count; 4, myeloproliferative diseases: common are primary thrombocytosis, true erythropoietic disease, chronic granulocytic leukemia, etc. will appear platelet increase. If the increase is only mild, between (300-600)×10^9/L, it usually does not have particularly serious consequences and should be reviewed regularly. If platelets are persistently greater than 600×10^9/L, various thrombotic diseases, such as bilateral lower extremity deep vein thrombosis, cerebral thrombosis and pulmonary embolism, are likely to occur and require early treatment.